Stamped fuel cell bipolar plate

ABSTRACT

A bipolar plate assembly for a fuel cell having a pair of stamped plates joined together to define a coolant volume therein. Each of the pair of stamped plates have a flow field arranged to maximize the contact area between the plates while allowing coolant to distribute and flow readily within the coolant volume. The bipolar plate assembly further includes a seal arrangement and integral manifold to direct gaseous reactant flow through the fuel cell.

TECHNICAL FIELD

[0001] This invention relates to a fuel cell stack assembly and moreparticularly to a bipolar plate assembly having a pair of stamped metalplates bonded together to provide coolant volume therebetween.

BACKGROUND OF THE INVENTION

[0002] Fuel cells have been proposed as a power source for manyapplications. One such fuel cell is the proton exchange member or PEMfuel cell. PEM fuel cells are well known in the art and include an eachcell thereof a so-called membrane-electrode-assembly or MEA having athin, proton conductive, polymeric membrane-electrolyte with an anodeelectrode film formed on major face thereof and a cathode electrode filmformed on the opposite major face thereof. Various membrane electrolytesare well known in the art and are described in such U.S. Pat. Nos.5,272,017 and 3,134,697, as well as in the Journal of Power Sources,vol. 29 (1990) pgs. 367-387, inter alia.

[0003] The MEA is interdisposed between sheets of porous gas-permeable,conductive material known as a diffusion layer which press against theanode and cathode faces of the MEA and serve as the primary currentcollectors for the anode and cathode as well as provide mechanicalsupport for the MEA. This assembly of diffusion layers and MEA arepressed between a pair of electronically conductive plates which serveas secondary current collectors for collecting the current from theprimary current collectors and for conducting current between adjacentcells internally of the stack (in the case of bipolar plates) andexternally of the stack (in the case of monopolar plates at the end ofthe stack). Secondary current collector plates each contain at least oneactive region that distributes the gaseous reactants over the majorfaces of the anode and cathode. These active regions also known as flowfields typically include a plurality of lands which engage the primarycurrent collector and define therebetween a plurality of grooves or flowchannels through which the gaseous reactant flow between a supply headerand a header region of the plate at one of the channel and an exhaustheader in a header region of the plate at the other end of the channel.In the case of bipolar plates, an anode flow field is formed on a firstmajor face of the bipolar plate and a cathode flow field is formed on asecond major face opposite the first major face. In this manner, theanode gaseous reactant (e.g., H₂) is distributed over the surface of theanode electric film and the cathode gaseous reactant (e.g., O₂/air) isdistributed over the surface of the cathode electrode film.

[0004] The various concepts of been employed to fabricate a bipolarplate having flow fields formed on opposite major faces. For example,U.S. Pat. No. 6,099,984 discloses bipolar plate assembly having a pairof thin metal plates with an identical flow field stamped therein. Thesestamped metal plates are positioned in opposed facing relationships witha conductive spacer interposed therebetween. This assembly of plates andspacers are joined together using conventional bonding technology suchas brazing, welding, diffusion bonding or adhesive bonding. Such bipolarplate technology has proved satisfactory in its gas distributionfunction, but results in a relatively thick and heavy bipolar plateassembly and thus impacts the gravimetric and volumetric efficiency ofthe fuel cell stack assembly.

[0005] In another example, U.S. Pat. No. 6,503,653 discloses a singlestamped bipolar plate in which the flow fields are formed in oppositemajor faces thereof to provide a non-cooled bipolar plate. A cooledbipolar plate using this technology again requires a spacer elementinterposed between a pair of stamped plates, thereby increasing thethickness and weight of the cooled plate assembly. U.S. Pat. No.6,503,653 takes advantage of unique reactant gas porting and staggeredseal arrangements for feeding the reactant gases from the header regionthrough the port in the plate to the flow field formed on the oppositeside thereof. This concept is very desirable in terms of cost but itsdesign constraints on flow fields may rule out some application.Furthermore, this design concept does not lend itself readily toproviding an internal cooling flow.

[0006] Applications with high powered density requirements need coolingin about every other fuel cell. Thus, there is an ever present desire torefine the design of a bipolar plate assembly to be efficiently used ina fuel cell stack to provide a high gravimetric power density, highvolumetric power density, low cost and higher, reliability. The presentinvention is directed to a stamped fuel cell bipolar plate that offerssignificant flow field design flexibility while minimizing the weightand thickness thereof.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to a bipolar plate assemblyhaving two thin metal plates formed with conventional stamping processesand then joined together. In another aspect, the centerlines of the flowfields must be arranged to align the channels for plates on oppositesides of the MEA wherever possible to further provide uniformcompression of the diffusion media. In another aspect, the configurationof the flow fields formed in each of the two stamped metal plates aresuch that the contact area therebetween is maximized to enable thebipolar plate assembly to carry compressive loads present in a fuel cellstack. Thus, the centerlines of the flow fields formed in the two thinmetal plates of a bipolar plate assembly need to be coincident in manyplaces to carry the compressive loads. However, since the interiorvolume defined between the plates and their context areas form aninterior cavity for coolant flow, it is necessary to have sufficientinstances where the centerlines are not coincident in order to allowadequate coolant flow. The present invention achieves these twoapparently opposing objections with a unique flow field design in whichajoining areas of the flow channels adjacent the inlet and exhaustmargins provide a geometric configurations to provide the desired flowfield and contact area requirements.

[0008] The present invention provides a bipolar plate assembly whichincludes a pair of plates having reactant gas flow fields defined by aplurality of channels formed the outer faces of the plates. The platesare arranged in a facing relationship to define an interior volumetherebetween. A coolant flow field is formed in an interior volumedefined between the pair of plates at the contact interfacetherebetween. The coolant flow field has an array of discrete flowdisruptors adjacent a coolant header inlet and a plurality of parallelchannels interposed between the array and the coolant exhaust header.Fluid communication is provided from the coolant inlet header throughthe coolant flow field to the coolant exhaust header.

[0009] The present invention also provides a separator plate whichincludes a thin plate having an inlet margin with a pair of lateralinlet headers and a medial inlet header formed therethrough, an exhaustmargin including a pair of lateral exhaust headers and a medial exhaustheader formed therethrough and a reactant gas flow field formed on amajor face of the thin plate. The reactant gas flow field includes afirst set of flow channels, each having an inlet leg with a firstlongitudinal portion in fluid communication with one of the pair oflateral inlet headers and a first transverse portion, a serpentine leghaving a first end in fluid communication with the first transverseportion and a second end and an exhaust leg having a second transverseportion in fluid communication with the second end of the serpentine legand a second longitudinal portion in fluid communication with one of thepair of lateral exhaust headers. Either of the transverse portion of theinlet leg adjacent the medial inlet header and the transverse portion ofthe exhaust leg adjacent the medial exhaust header may be defined by anundulating flow channel.

[0010] These and other aspects of the present invention provide abipolar plate assembly which increases the design flexibility in termsof flow field options, while achieving the cooling requirements as wellas providing a relatively high gravimetric power density and highvolumetric power density from a fuel cell stack incorporating thebipolar plate assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will be better understood when considered in thelight of the following detailed description of a specific embodimentthereof which is given hereafter in conjunction with the several figuresin which:

[0012]FIG. 1 is a schematic isometric exploded illustration of a fuelcell stack;

[0013]FIG. 2 is an isometric exploded illustration of a bipolar plateassembly and seal arrangement in accordance with the present invention;

[0014]FIG. 3 is a plan view of the flow field formed in the major faceof an anode plate in the bipolar plate assembly shown in FIG. 2;

[0015]FIG. 4 is a plan view of the flow field formed in the major faceof a cathode plate in the bipolar plate assembly shown in FIG. 2;

[0016]FIG. 5 is a plan view showing the contact areas at the interfacebetween the anode and cathode plates;

[0017]FIG. 6 is an isometric view of multiple cells within the fuel cellstack and further showing a section taken through the cathode header;

[0018]FIG. 7 is a cross-section taken through the coolant header andshowing the coolant flow path;

[0019]FIG. 8 is a cross-section taken through the anode header andshowing the anode gas flow path; and

[0020]FIG. 9 is a cross-section taken through the cathode header andshowing the cathode flow path.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. With reference to FIG. 1, a two-cell stack(i.e., one bipolar plate) is illustrated and described hereafter, itbeing understood that a typical stack will have many more such cells andbipolar plates. FIG. 1 depicts a two-cell bipolar PEM fuel cell stack 2having a pair of membrane-electrode-assemblies (MEAs) 4, 6 separatedfrom each other by an electrically conductive, liquid-cooled bipolarplate 8. The MEAs 4, 6 and bipolar plate 8 are stacked together betweenclamping plates 10, 12 and monopolar end plates 14, 16. The clampingplates 10, 12 are electrically insulated from the ends plate 14, 16. Theworking face of each monopolar end plates 14, 16, as well as bothworking faces of the bipolar plate 8 contain a plurality of grooves orchannels 18, 20, 22, 24 defining a so-called “flow field” fordistributing fuel and oxidant gases (i.e., H₂ and O₂) over the faces ofthe MEAs 4,6. Nonconductive gaskets 26, 28, 30 and 32 provide seals andelectrical insulation between the several components of the fuel cellstack. Gas-permeable diffusion media 34, 36, 38, 40 press up against theelectrode faces of the MEAs 4, 6. The end plates 14, 16 press up againstthe diffusion media 34, 40 respectfully, while the bipolar plate 8presses up against the diffusion media 36 on the anode face of MEA 4,and against the diffusion media 38 on the cathode face of MEA 6.

[0022] With reference to FIG. 2, the bipolar plate assembly 8 includestwo separate metal plates 100, 200 which are bonded together so as todefine a coolant volume therebetween. The metal plates 100, 200 are madeas thin as possible (e.g., about 0.002-0.02 inches thick) and arepreferably formed by suitable forming techniques as is known in the art.Bonding may, for example, be accomplished by brazing, welding diffusionbonding or gluing with a conductive adhesive as is well known in theart. The anode plate 100 and cathode plate 200 of a bipolar plateassembly 8 are shown having a central active region that confronts theMEAs 36, 38 (shown in FIG. 1) and bounded by inactive regions ormargins.

[0023] The anode plate 100 has a working face with an anode flow field102 including a plurality of serpentine flow channels for distributinghydrogen over the anode face of the MEA that it confronts. Likewise, thecathode plate 200 has a working face with a cathode flow field 202including a plurality of serpentine flow channels for distributingoxygen (often in the form of air) over the cathode face of the MEA thatit confronts. The active region of the bipolar plate 8 is flanked by twoinactive border portions or margins 104, 106, 204, 206 which haveopenings 46-56 formed therethrough. When the anode and cathode plates100, 200 are stacked together, the openings 46-56 in the plates 100, 200are aligned with like openings in adjacent bipolar plate assemblies.Other components of the fuel cell stack 2 such as gaskets 26-32 as wellas the membrane of the MEAs 4 and 6 and the end plates 14, 16 havecorresponding openings that align with the openings in the bipolar plateassembly in the stack, and together form headers for supplying andremoving gaseous reactants and liquid coolant to/from the stack.

[0024] In the embodiment shown in the figures, opening 46 in a series ofstacked plates forms an air inlet header, opening 48 in series ofstacked plates forms an air outlet header, opening 50 in a series ofstacked plates forms a hydrogen inlet header, openings 52 in a series ofstacked plates forms a hydrogen outlet header, opening 54 in a series ofstacked plates forms a coolant inlet header, and opening 56 in a seriesof stacked plates forms a coolant outlet header. As shown in FIG. 1,inlet plumbing 58, 60 for both the oxygen/air and hydrogen are in fluidcommunication with the inlet headers 46, 50 respectively. Likewise,exhaust plumbing 62, 64 for both the hydrogen and the oxygen/air are influid communication with the exhaust headers 48, 52 respectively.Additional plumbing 66, 68 is provided for respectively supplying liquidcoolant to and removing coolant from the coolant header 54, 56.

[0025]FIG. 2 illustrates a bipolar plate assembly 8 and seals 28, 30 asthey are stacked together in a fuel cell. It should be understood that aset of diffusion media, an MEA, and another bipolar plate (not shown)would underlie the cathode plate 200 and seal 30 to form one completecell. Similarly, another set of diffusion media and MEAs (not shown)will overlie the anode plate 100 and seal 28 to form a series ofrepeating units or cells within the fuel cell stack. It should also beunderstood that an interior volume or coolant cavity 300 is formeddirectly between anode plate 100 and cathode plate 200 without the needof an additional spacer interposed therebetween.

[0026] Turning now to FIG. 3, a plan view of the anode plate 100 isprovided which more clearly shows the anode flow field 102 formed in theworking face of anode plate 100. As can also be clearly seen in FIG. 3,the inlet margin 104 of anode plate 100 has a pair of lateral inletheaders 46 and 50 to transport cathode gas and anode gas, respectively,through the fuel cell stack and a medial inlet header 54 to transport acoolant through the stack. Similarly, the exhaust margin 106 has a pairof lateral exhaust headers 48, 52 for transporting anode affluent andcathode affluent, respectively through the fuel cell stack, and a medialexhaust header 56 for transporting coolant through the fuel cell stack.

[0027] The anode flow field 102 is defined by a plurality of channelsformed to provide fluid communication along a tortuous path from theanode inlet header 50 to the anode exhaust header 52. In general, theflow channels are characterized by an inlet leg 108 having alongitudinal portion 110 with a first end in fluid communication withthe anode inlet header 50 and a second end in fluid communication with atransverse portion 112. As presently preferred, the transverse portion112 of the inlet leg 108 branches to provide a pair of transverse inletlegs associated with each longitudinal portion 110. Furthermore, thepath of these transverse inlet portions 112 undulate within the plane ofthe anode plate 100 to provide an undulating flow channel adjacent thecoolant inlet header 54 as represented in the area designated 114. Thetransverse portion 112 of inlet leg 108 is in fluid communication with aserpentine leg 116. The flow channel 108 further includes an exhaust leg118 having transverse portions 120 and a longitudinal portion 122 toprovide fluid communication from the serpentine leg 116 to the anodeexhaust header 52. The exhaust leg portion 118 is configured similar tothe inlet leg portion 108 in that each longitudinal portion 122 isassociated with a pair of transverse portions 120. The path of thetransverse exhaust portions 120 undulate within the plane of the anodeplate 100 to provide an undulating flow channel adjacent the coolantexhaust header 56 as represented in the area designated 124.

[0028] Turning now to FIG. 4 a plan view of the cathode plate 200 isprovided which more clearly shows the cathode flow field 202 formed inthe working face of cathode plate 200. As can also be clearly seen inFIG. 4, the inlet margin 204 of cathode plate 200 has a pair of lateralinlet headers 46, 50 to transport cathode gas and anode gas,respectively, through the fuel cell stack and a medial inlet header 54to transport a coolant through the stack. Similarly, the exhaust margin206 has a pair of lateral exhaust headers 48, 52 for transporting anodeaffluent and cathode affluent, respectively through the fuel cell stack,and a medial exhaust header 56 for transporting coolant through the fuelcell stack.

[0029] The cathode flow field 202 is defined by a plurality of channelsformed to provide fluid communication along a tortuous path from thecathode inlet header 46 to the cathode exhaust header 48. In general,the flow channels are characterized by an inlet leg 208 having alongitudinal portion 210 with a first end in fluid communication withthe cathode inlet header 46 and a second end in fluid communication witha transverse portion 212. A single transverse portion 212 is associatedwith each longitudinal portion 210. Thus, the transverse portion 212 ofthe inlet leg 208 does not branch off to provide a pair of transverseinlet portions as the transverse portion 112 of anode inlet leg 108. Thepath of the transverse inlet portions 212 undulate within the plane ofthe cathode plate to provide an undulating flow channel adjacent thecoolant inlet header 54 as represented in the area designated 214. Theflow channel further includes a serpentine leg 216 which is in fluidcommunication with the end of transverse inlet portion 212. The flowchannel further includes an exhaust leg 218 having a transverse portion220 and a longitudinal portion 222. The exhaust leg portion 218 isconfigured similar to the inlet leg portion 208 to provide fluidcommunication from the serpentine leg 216 to the cathode exhaust header48. The path of the transverse exhaust portions 220 undulate within theplane of the cathode plate to provide an undulating flow channeladjacent the coolant exhaust header 56 as represented in the areadesignated 224.

[0030] Referring now to FIGS. 2 and 6, the anode plate 100 and thecathode plate 200 are positioned in an opposed facing relationship suchthat the various inlet and exhaust headers are in alignment. The anodeplate 100 and the cathode plate 200 are then joined together usingconventional techniques. The centerlines of the anode flow fields 102and cathode flow fields 202 are arranged to align the flow channels onopposing plates (e.g. on opposite sides of the MEA as shown in FIG. 6)wherever possible to provide uniform compression of the diffusion mediaand the MEA. Likewise, the contact area between the adjacent, joinedanode plate 100 and cathode plate 200 (as shown in FIG. 2) arecoincident in many places so as to carry the compressive loads imposedon the fuel cell stack. Specifically, the flow channels of anode flowfield 102 formed in the working face of anode plate 100 provide acomplimentary contact surface on an inner face opposite the workingface. Similarly, the flow channels of the cathode flow field 202 formedin the working face of the cathode plate 200 define a contact surface onan inner face of the cathode plate 200. Thus, when the anode plate 100and cathode plate 200 are joined together, an interference or contactarea is defined therebetween.

[0031] With reference now to FIG. 5, the contact area between the anodeplate 100 and the cathode plate 200 defines a coolant flow field 302between an inlet margin 304 and an exhaust margin 306 within coolantcavity 300. The coolant flow field 302 includes an array of discreteflow disruptors 308 adjacent the coolant inlet manifold 54 formed at theinterface of the anode inlet legs 108 and the cathode inlet legs 208.Similarly, a set of flow disrupters 310 are formed adjacent the coolantexhaust header 56 at the interface of the anode exhaust leg 118 and thecathode exhaust legs 218. The coolant flow field 302 further includes aplurality of parallel of flow channels 312 interposed between the inletmargin 304 and the exhaust margin 306 which are defined at the interfaceof the serpentine legs 116 and the serpentine legs 216. In accordancewith the configuration of the anode flow field 102 and cathode flowfield 202, the array of discrete flow disruptors 308 extend obliquelyfrom the area of the coolant flow field 302 adjacent the coolant inletheader 54 as indicated by directional arrow 314 into the parallel flowchannels 312. Likewise, the array of discrete flow disruptors 310 extendfrom the parallel flow channels 312 obliquely towards the coolantexhaust header 56 as indicated by directional arrow 316.

[0032] Turning now to FIGS. 6-9, the present invention incorporates astaggered seal and an integral manifold configuration for directingfluid communication from the header into the appropriate flow field. Forexample, the location of the seal beads between the inlet margin 104,204 and the flow field structure 102, 202 step left and right (as seenin FIGS. 7-9) for each successive layer. Thus, the seal position shiftsto provide fluid communication therebetween. Ports in the form of holesor slots penetrate vertically through the anode plate 100 or cathodeplate 200 to provide means for fluid communication from the header tothe flow field. In this manner, the present invention employs astaggered seal concept similar to that disclosed in U.S. Pat. No.6,503,653, which is commonly owned by the assignee of the presentinvention and whose disclosure is expressly incorporated by referenceherein. This approach allows the combined seal thicknesses to equal therepeat distance minus the thickness of the anode plate and cathodeplate. This approach also provides an advantage over other conventionalfuel cell stack design in which the thickness available for seals isreduced by the height required for the fluid passage from the headerregion to the active area region. By utilizing a staggered seal concept,the present invention affords the use of thicker seals which are lesssensitive to tolerance variations.

[0033] The present invention further improves upon the staggered sealconcept disclosed in U.S. Pat. No. 6,503,653 with the use of separateanode plate 100 and cathode plate 200 in each bipolar plate assembly.Specifically, a second plate enables the use of an integral manifoldwith the space between the plates. Reactant gases or coolant fluid cannow enter on the top side of the upper plate, travel between the upperand lower plate through such integral manifolds and then enter the lowerside of the upper plate to feed the bottom side of the MEA. As a result,the width of the region where the reactant gases enter the flow field istwice as wide as that disclosed in U.S. Pat. No. 6,503,653, therebylowering the overall pressure drop across a given flow field. Thisaspect of the present invention is best illustrated in FIGS. 7-9.Specifically, as illustrated in FIG. 7, the coolant flow path isindicated by the arrows A showing flow from the coolant header (notshown) between the anode plate 100 and the cathode plate 200 and intothe coolant flow field 302 defined therebetween. Similarly, in FIG. 8the anode gas flow path is indicated by the arrows B showing flow fromthe anode header (not shown) between the cathode plate 200 and the anodeplate 100 and into the anode flow field 102. Similarly, in FIG. 9 thecathode gas flow path is indicated by the arrows C showing flow from thecathode header (not shown) between the anode plate 100 and the cathodeplate 200 and into the cathode flow field 202. In this manner, a widermanifold region is provided between the header region and the flow fieldregion for each of the fluids passed through the fuel cell stack.

[0034] As presently preferred, the design of the bipolar plate assemblyfurther includes an additional feature to support the seal loads giventhe effect of widening the inlet manifold region between the headers andthe active flow fields. Specifically, as best seen in FIGS. 4 and 6 anin-situ support flange 226 extends transversely across the inlet marginthrough the cathode inlet header 46, the coolant inlet header 54 and theanode header 50. This support flange 226 is formed with a wavy orcorrugated configuration to allow inlet fluids to freely pass from theheader region through the manifold region into the flow field regionwhile at the same time providing through plane support for the bipolarplate assembly. For example, as best seen in FIG. 6, the support flange226 for the cathode plate 200 of the bipolar plate 8 occurs directlyover the support flange 126 for the anode plate 100 of the neighboringcell. In this manner, compressive loads are readily transmitted throughthe fuel cell stack. Alternately, the support function could be providedwith grooved blocks of a non-conductive material or similar featureswhich could be formed in the seals to replace the in-situ configurationprovided by the transverse support flange.

[0035] When using this configuration, these adjacent regions must beinsulated since they are at different electrical potentials. Varioussuitable means are available such as the use of a non-conductive coatingsuch as that disclosed in U.S. application Ser. No. 10/______ (AttorneyDocket No. GP301598) entitled “Fuel Cell Having Insulated CoolantManifold” filed on Apr. 25, 2002 which is commonly owned by the assigneeof the present invention and the disclosure of which is expresslyincorporated by reference. Alternately, a film of non-conductive plastictape my be interposed for providing electrical isolation therebetween.

[0036] The present invention provides a two piece bipolar plate assemblyhaving a coolant flow field formed therebetween. The configuration ofthe various flow fields are such that the bipolar plate assembly may bea formed of relatively thin material, and still support the requiredcompressive loads of the fuel cell stack. Furthermore, the presentinvention provides much greater design flexibility in terms of flowfield options. In this regard, the present invention provide animprovement in the gravimetric and volumetric power densities of a givenfuel cell stack as well as significant material and cost savings.

[0037] The description of the invention set forth above is merelyexemplary in nature and, thus, variations that do not depart from thejest of the invention are intended to be within the scope of theinvention. Such variations are not to be regarded as a departure fromthe spirit and scope of the invention.

What is claimed is:
 1. A bipolar plate assembly for a fuel cell including a pair of plates having a first margin with a first header formed therein and a second margin with a second header formed therein, said bipolar plate assembly comprising: a first plate of said pair of plates having a first flow field defined by a plurality of channels formed on a first outer face thereof and a first contact surface on a first inner face thereof; a second plate of said pair of plates having a second flow field defined by a plurality of channels formed on a second outer face thereof and a second contact surface on a second inner face thereof, said second inner face being arranged in facing relationship with respect to said first inner face; a third flow field defined by direct contact between said first contact surface and said second contact surface, said third flow field having an array of discrete flow disruptors adjacent said first header and a plurality of parallel channels interposed between said array of flow disruptors and said second header; wherein fluid communication is provided from said first header through said third flow field to said second header.
 2. The bipolar plate assembly of claim 1 wherein said array of discrete flow disruptors comprises a first set of flow disruptors adjacent said first header and a second set of flow disruptors extending obliquely into said plurality of parallel channels.
 3. The bipolar plate assembly of claim 2 wherein said array of discrete flow disruptors further comprises a third set of flow disruptors extending obliquely into said plurality of parallel channels in an direction opposite said second set of flow disruptors.
 4. The bipolar plate assembly of claim 1 wherein said third flow field further comprises a second array of discrete flow disruptors interposed between said plurality of parallel channels and said second header.
 5. The bipolar plate assembly of claim 4 wherein each of said first and second arrays comprise a first set of flow disruptors adjacent said first and second headers respectively and a second set of flow disruptors extending obliquely into said plurality of parallel channels.
 6. The bipolar plate assembly of claim 5 wherein each of said first and second arrays further comprises a third set of flow disruptors extending obliquely into said plurality of parallel channels in an direction opposite said second set of flow disruptors.
 7. The bipolar plate assembly of claim 1 further comprising a first seal disposed on said outer face of said first plate and cooperating therewith to provide a first fluid communication path between a third header formed in said first margin and said first flow field and a second fluid communication path between said first flow field and a fourth header formed in said second margin.
 8. The bipolar plate assembly of claim 7 further comprising a second seal disposed on said outer face of said second plate and cooperating therewith to provide a third fluid communication path between a fifth header formed in said first margin and said second flow field and a fourth fluid communication path between said second flow field and a sixth header formed in said second margin.
 9. A separator plate for a bipolar plate assembly for a fuel cell comprising a thin plate having an inlet margin including a pair of reactant gas inlet headers and a coolant inlet header formed therethrough, an exhaust margin including a pair of reactant gas exhaust header and a coolant exhaust header formed therethrough and a flow field formed on a major face of said thin plate, said flow field including a first set of flow channels, each of said first set of flow channels having an inlet leg with a first longitudinal portion in fluid communication with one of said pair of reactant gas inlet headers and a first transverse portion, a serpentine leg having a first end in fluid communication with said first transverse portion and a second end and an exhaust leg having a second transverse portion in fluid communication with said second end of said serpentine leg and a second longitudinal portion in fluid communication with one of said pair of reactant gas exhaust header, wherein at least one of said first transverse portion of said inlet leg adjacent said coolant inlet header and said second transverse portion of said exhaust leg adjacent said coolant exhaust header defines an undulating flow channel.
 10. The separator plate of claim 9 wherein said undulating flow channel in said first set of flow channels is formed in said first transverse portion of said inlet leg.
 11. The separator plate of claim 9 wherein said undulating flow channel in said first set of flow channels is formed in said second transverse portion of said exhaust leg.
 12. The separator plate of claim 9 wherein said undulating flow channel comprises at least two undulations.
 13. The separator plate of claim 9 wherein said pair of reactant gas inlet headers are located laterally on either side of said coolant inlet header and said pair of reactant gas exhaust headers are located laterally on either side of said coolant exhaust header.
 14. The separator plate of claim 9 wherein said flow field further comprises a second set of flow channels, each of said second set of flow channels having an inlet leg with a first longitudinal portion in fluid communication with said one of said pair of reactant gas inlet headers and a first transverse portion, a serpentine leg having a first end in fluid communication with said first transverse portion and a second end and an exhaust leg having a second transverse portion in fluid communication with said second end of said serpentine leg and a second longitudinal portion in fluid communication with said one of said pair of reactant gas exhaust headers, wherein at least one of said first transverse portion of said inlet leg adjacent said coolant inlet header and said second transverse portion of said exhaust leg adjacent said coolant exhaust header defines an undulating flow channel.
 15. The separator plate of claim 14 wherein said undulating flow channel in said second set of flow channels is formed in said first transverse portion of said inlet leg.
 16. The separator plate of claim 14 wherein said undulating flow channel in said second set of flow channels is formed in said second transverse portion of said exhaust leg.
 17. The separator plate of claim 14 wherein said undulating flow channel comprises at least two undulations.
 18. The separator plate of claim 14 wherein said pair of reactant gas inlet headers are located laterally on either side of said coolant inlet header and said pair of reactant gas exhaust headers are located laterally on either side of said coolant exhaust header.
 19. The separator plate of claim 9 wherein each of said first set of flow channels further comprise a third transverse portion having a first end in fluid communication with said first longitudinal portion, a second serpentine leg having a first end in fluid communication with said third transverse portion and a second end and a fourth transverse portion in fluid communication with said second end of said second serpentine leg and said second longitudinal portion, wherein at least one of said third transverse portion of said inlet leg adjacent said coolant inlet header and said fourth transverse portion of said exhaust leg adjacent said coolant exhaust header defines an undulating flow channel. 